This isn't as hard as you might think.
You score 10,000 points for every boss level
7,500 for every bonus level
and for every regular level you clear you get 5,000
And as everyone has pointed out you get combo bonuses for hitting consecutive blocks.
What I found and what I used to my advantage is once you hit the unlock block you can move between the levels up or down. the only exception would be the boss levels and the first level after the boss.
If the levels are cleared except for a couple regular blocks you can keep hitting the unlock block to get a good multiplier going. Once you get bored of bouncing between levels or if you clear all the blocks just move on. If you clear all the blocks in a level the unlock block won't come back.
Using this method I was able to hit 1,000,000 points after I beat the level 36 boss.